We have a number of questions here about E2 vs. E4 airspace (see summary of links in [this answer][1]) but what does that mean? As far as I can see, neither the AIM nor the ATC Orders mention E2 or E4 airspace, so what are they? What are the practical differences for pilots and controllers?


  [1]: https://aviation.stackexchange.com/a/64210/62